In the silicon oxide film coating step by moisture oxidation process in the semi-conductor production, for example, super high-purity water vapor is required at the rate of some 1,000 cubic centimeters/minute (sccm).
Earlier, the inventors developed a reactor for generation of water which was suitable for such a purpose, the construction of which is shown in FIG. 13. It should be understood that this reactor will be referred to as prior art reactor throughout the present specification.
As shown in FIG. 13, the prior art reactor includes a reactor shell 21 comprising bottomed cylindrical first and second reactor structural components 22 and 23 put together, the first reactor structural component 22 provided with a gas feed passage 24a on the outside surface thereof and an inlet reflector unit 29a on the inside surface thereof, and the second reactor structural component 23 provided with a (water vapor) outlet passage 25a on the outside surface thereof and an outlet reflector unit 29b on the inside surface thereof, with a diffusion filter 30 provided on the borderline between the two reactor structural components 22 and 23 and with a platinum coated catalyst layer provided over the inside surface of the second reactor structural component 23.
In the prior art reactor, a starting material gas comprising a mixture of hydrogen and oxygen is led into the reactor shell through the gas feed passage 24a is diffused by a gas diffusion means comprising the inlet reflector 29a, the diffusion filter 30 and the outlet reflector 29b and brought into contact with the platinum coated catalyst layer 32. Coming in contact with the platinum coated catalyst layer 32, oxygen and hydrogen are enhanced in reactivity by the catalytic action of platinum and turned into what is called the radicalized state. The radicalized hydrogen and oxygen instantaneously react at a temperature much lower than the ignition temperature of the hydrogen-mixed gas under formation of water without undergoing combustion at a high temperature.
FIG. 14 shows the change with time in moisture-producing reactivity found in an experiment with the prior art reactor operated under the following conditions: moisture production, 1,000 sccm; and reactor temperature (temperature inside the reactor shell 21), about 400.degree. C. The volume of the space provided with the platinum coated catalyst layer 32 (volume inside the second reactor structural component) was about 490 cc. As is evident from FIG. 14, the prior art reactor can produce water vapor at a moisture-producing reactivity efficiency of some 98.5 to 99.9 percent not only where the mixing ratio of the starting material gas between oxygen and hydrogen is optimized (with no excess of either of the two material constituent gases) but also where the mixed gas contains more oxygen or hydrogen than the other.
Thus, the prior art reactor can produce more than 1,000 sccm of water vapor (high-purity water vapor or mixture of high-purity water vapor and oxygen) with a high degree of reactivity and responsiveness and is suitable for use in the semi-conductor manufacturing technological field. The reactor also allows size reduction of the moisture-producing facilities.
However, it has been found that the prior art reactor still leaves something to be improved. That is, the prior art can not raise the moisture-producing reactivity efficiency over 99.0 percent when the temperature of the reactor shell 21 is less than some 400.degree. C. with the moisture production not lower than 1,000 scm. And it is feared that some one percent of unreacted oxygen or hydrogen will be mixed in the moisture produced. That makes it difficult for the reactor to reliably turn out pure water without hydrogen or oxygen mixed or a mixture of pure water and oxygen without hydrogen mixed.
Meanwhile, there are two probable causes of unreacted hydrogen or oxygen reaching the water vapor outlet passage 25a in the prior art reactor: (a) Oxygen or hydrogen flows direct into the water vapor outlet passage 25a without coming in contact with the platinum coated catalyst layer 32. (b) Hydrogen or oxygen is radicalized but proceeds unreacted with oxygen or hydrogen straight to the water vapor outlet passage 25a where the radicalized hydrogen or oxygen is unradicalized back to the original state. Of the two probable causes, it was thought that the first one was overwhelmingly greater according to various experiments conducted by the inventors and their experiences. So, the inventors carried out a moisture-producing experiment to study the moisture-generating reactivity efficiency using the prior art reactor with the outlet reflector unit 29b removed. As shown in FIG. 15, the moisture-producing reactivity efficiency stood at about 91 percent when the temperature of the reactor shell 21 was 400.degree. C. with the moisture production at 500 sccm with the mixed material gas with an optimized mixing ratio. While the test results were not obtained under exactly the same conditions for those shown in FIG. 14 because the moisture production was different, it is noted that the moisture-producing reactivity efficiency is some 7 percent lower than that shown in FIG. 14. This difference indicates that, without the reflector unit 29b on the outlet side, a substantial amount of oxygen or hydrogen arrives unradicalized at the moisture gas outlet passage 25a and that an improvement of the reflector unit 29b on the outlet reflector unit 29b could increase the moisture-producing reactivity efficiency. Also, as FIG. 15 suggests, if the reflector unit 29b is absent on the outlet side, the moisture-producing reactivity efficiency goes down as the percentage of hydrogen in the material gas increases. When the temperature of the reactor shell is 400.degree. C. with the moisture production at 500 sccm, for example, the moisture-producing reactivity efficiency is some 86 percent with the starting material gas with the hydrogen content being 100 percent larger than the balanced level and some 97 percent with the material gas with the oxygen content being 100 percent larger. The difference in efficiency between the two mixing ratios is some 11 percent.
That is, it is surmised that oxygen diffuses with relative ease and tends not to move in a straight line, while hydrogen is rather difficult to diffuse and tends to flow linearly inside the reactor shell 21 of the construction as shown in FIG. 13. With hydrogen-rich starting material gas, therefore, it is considered that the tendency for hydrogen to flow linearly is so strong that oxygen is swept along with the hydrogen and reaches the water vapor outlet passage 25a unradicalized to a great extent.
Based on that theory, the inventors concluded that if the outlet reflector unit 29b in the reactor shell 21 was so improved as to enhance the diffusion of especially hydrogen, still a higher yield than the moisture producing reactivity efficiency or reaction rate of some 98 to 99 percent shown in FIG. 14 could be achieved not only with oxygen-rich starting material gas but also with hydrogen-rich starting material gas.
The present invention was built on that theory.